Annular acoustic arrays generally include a group of concentric rings of a piezoelectric or ferro-electric material which are mounted precisely concentric on a lens. The phase of operation of the different rings can be closely controlled to transmit or receive sound from a particular depth. It is often advantageous to divide the rings into segments so the direction of focus can be shifted sidewardly.
The manufacture of an annular phased array is complicated by the difficulties of cutting and machining the brittle piezoelectric materials that are used. The manufacture of such arrays is an active area of investigation. A simple method of fabrication is to apply an electrode to the back of the crystal plate in the pattern desired, to etch away the pattern to a depth just short of the opposite face of the plate. However, the ring elements are still mechanically attached at their front face, which degrades the performance of the resulting transducer. Separate rings have been machined, but it is difficult and time consuming to position the rings precisely concentric on a lens. The difficulty increases where each ring is formed in segments. A low cost method for forming piezoelectric rings, especially in segments, and mounting them precisely concentric on a lens, with each ring or segment being substantially isolated from adjoining rings and segments, would be of considerable value.